RESEARCH ARTICLE A. Quetglas Æ M. Gonza´lez Æ I. Franco Biology of the upper-slope cephalopod Octopus salutii from the western Mediterranean Sea Received: 6 July 2004 / Accepted: 15 November 2004 / Published online: 19 January 2005 Ó Springer-Verlag 2005 Abstract A total of 310 individuals (124 males, 185 fe- males, 1 indeterminate) of the octopod Octopus salutii caught throughout the year by bottom trawlers from 25 to 800 m depth in the western Mediterranean were analysed to study some general aspects of its biology. Octopus sizes ranged from 4.0 to 13.0 cm ML and 3.5 to 16.5 cm ML in males and females, respectively. The species inhabits the lower continental shelf and upper slope, primarily between 250 and 500 m depth. The scarcity of small-sized individuals in the samples and the predominance of males and females >8 and >9 cm ML, respectively, suggest two interpretations: (1) juve- niles inhabit grounds inaccessible to, or unsampled by, trawlers, or they avoid capture owing to behavioural aspects; or (2) the species meet in the trawling grounds for reproduction, because in the sizes described the majority of individuals have begun sexual maturation. The reproductive period was found to occur during spring and summer. The stomach content analysis re- vealed a diet composed of 33 different prey items belonging to three major taxonomic groups (crusta- ceans, fishes and cephalopods). Quantitatively, crusta- ceans (Decapoda Reptantia and Natantia groups) were the most important prey, appearing in 87% of the stomachs, followed by fish (25%) and cephalopods (10%). Finally, the paper presents data on mantle length–total weight, gonad weight–total weight and lig- ulae length–total weight relationships, and utilises dif- ferent indexes (gonadosomatic, hepatosomatic, fullness weight and emptiness) to describe changes through the three maturity stages of both sexes. Introduction The octopus Octopus salutii (Verany, 1836) occurs throughout the Mediterranean Sea and also in the east Atlantic, where to date it has been reported from the Gulf of Biscay (Mangold-Wirz et al. 1976) to the Gulf of Cadiz (Guerra1982). In the western Mediterranean, the species inhabits mainly the lower continental shelf and upper slope (Quetglas et al. 2000; Gonza´lez and Sa´n- chez2002), where it is caught by trawlers targeting the hake (Merlucciusmerluccius) and the Norwegian lobster (Nephropsnorvegicus). Depending on the area, this octopus has either no or scarce commercial interest (Sartor et al. 1998), which is probably due to the poor consistency of its mantle. The biology of O. salutii is presently poorly known, with the only scientific paper devoted specifically to the species having been done nearly 30 years ago by Mangold-Wirz et al. (1976). These authors studied the reproductive biology of individuals maintained in the laboratory and extended the known distribution of the species from the Mediterranean, where it was for- merly thought to be confined, to the Atlantic. In an earlier work, Mangold-Wirz (1963) included the species in her revision of demersal cephalopods from the Cat- alan Sea, analysing their general biology and focusing on such aspects as annual distribution, growth and reproduction. The worldwide lack of information on the majority of deep-sea cephalopods is well known (Voss and Pearcy1990; Collins et al. 2001), and is related to their minimal commercial value and to the difficulty in capturing specimens at great depths. In the present paper, some aspects of the biology of the upper slope octopod O. salutii, taken throughout the year by Communicated by S.A. Poulet, Roscoff A. Quetglas (&) Centre Oceanogra`fic de Balears, IEO, Apt. 291, 07015 Palma de Mallorca, Spain E-mail: toni.quetglas@ba.ieo.es Fax: +34-971404945 M. Gonza´lez Æ I. Franco Centro Oceanogra´fico de Murcia, IEO, Apt. 22, San Pedro del Pinatar, 30740 Murcia, Spain Marine Biology (2005) 146: 1131–1138 DOI 10.1007/s00227-004-1522-4